Array antennas are antennas that include a number of radiating elements arranged in a predefined pattern that act collectively to generate an antenna pattern. Some array antennas, known as phased arrays, have beams that may be controllably steered by varying phase values associated with the elements of the array. An antenna pattern of an array antenna may have a main beam and one or more side beams or side lobes. Often, the side lobes are considered undesirable. In many receiver-based applications, only signals received through the main beam of an array antenna are of interest. For example, in a radar system that derives information about a remote target from one or more return pulses received from the target, the receiver may only be interested in processing pulses received through the main beam of the receive antenna. Likewise, in some communication systems, a receiver may only be interested in signals received from a particular direction and may wish to reject signals received from other directions.
A guard antenna is an antenna that works in conjunction with an array antenna to determine whether signals received through the array antenna were received through a main beam of the antenna or through a side lobe of the antenna. Techniques and structures are needed for implementing guard array antennas that are effective and easy to use.